Injection of micro-quantities of soluble drug is used extensively throughout the world for a wide range of drugs, reagents and biological substances. Many of these reagents are unstable in their liquid form under various conditions. An effective method for maintaining these unstable drugs in a stable condition is to keep the reagent as a dry formulation.
Current methods for administering dry formulations into patients involves adding a liquid diluent into a vial containing the dry reagent to be administered. The dry reagent is allowed to dissolve within the vial. This frequently requires some minimal agitation. Too much agitation can result in foaming of the reagent and preventing recovery of the appropriate amount of drug to administer to the patient. Following dissolution of the reagent, the reagent solution is withdrawn from the vial in a syringe. This charged syringe is then used to inject the patient. To assure that the proper amount of reagent is delivered, it is desirable to be able to view the reagent as it is administered.
One type of device for administering liquid drugs to a patient is the single-use syringe design described in U.S. Pat. No. 5,222,948. This device provides a means of a single use injection with a one way valve system that incorporates a needle and a separate solution chamber. The reagent to be delivered is contained as a solution within the solution chamber. For many applications, the reagent should remain stable in solution over relatively long periods of storage and/or transportation. Unfortunately, many reagents that could be delivered from this device are not stable in solution. Such reagents are, as a rule, considerably more stable as a dry form, i.e., powder or lyophilized.